1. Field of the Invention
The present invention relates generally to catalyst monitoring in a motor vehicle and, more particularly, to a method and apparatus for monitoring catalyst efficiency in a catalytic converter based on frequency characteristics of the catalyst as measured by oxygen sensors.
2. Discussion
Catalytic converters are used to reduce major air pollutants, such as hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NO.sub.x), contained in the exhaust gas from an internal combustion engine of a motor vehicle. Each converter contains catalysts that produce a heated chemical reaction that transforms noxious pollutants into less harmful carbon dioxide (CO.sub.2) and water (H.sub.2 O) vapors. The catalytic converter is integrated downstream from the vehicle's engine into the vehicle's exhaust system. The effectiveness of reducing pollutants by a catalytic converter is highly dependent on the temperature and total gas throughput which, in turn, depends on the operational states and conditions of the internal combustion engine. Over time, catalyst efficiency degrades and thus decreases the capacity of the converter to convert toxic material. Government environmental regulations require continued reductions in vehicle emissions as well as accurate monitoring of various components of the emission system.
Therefore, it would be desirable to provide a non-intrusive method for monitoring catalytic converter efficiencies that is not dependent on any special vehicle operating conditions. In this way, catalyst monitoring can be performed under steady-state and transient vehicle operating conditions. Catalyst monitoring should linearly correlate its algorithm output to catalyst efficiency. In addition, it should be performed with minimal processing requirements and no additional sensors or circuitry as provided by a typical motor vehicle.